Seed functional ecology in Brazilian rock outcrop vegetation: an integrative synthesis

Rock outcrop vegetation is distributed worldwide and hosts a diverse and unique flora that evolved under harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding seed traits, germination responses to abiotic factors and the potential role of phylogenetic relatedness in shaping such features. Here, we provide the first quantitative and phylogenetically informed synthesis of the seed functional ecology of Brazilian rock outcrop vegetation, with a particular focus on quartzitic and ironstone campo rupestre.

Using a database of functional trait data, we calculated the phylogenetic signal for seven seed traits for 371 taxa and tested whether they varied among growth forms, geographic distribution and microhabitats. We also conducted meta-analyses that included 4252 germination records for 102 taxa to assess the effects of light, temperature and fire-related cues on the germination of campo rupestre species and explored how the aforementioned ecological groups and seed traits modulate germination responses.

All traits and germination responses showed a moderate to strong phylogenetic signal. Campo rupestre species responded positively to light and had maximum germination between 20 and 25 °C. The effect of temperatures beyond this range was moderated by growth form, species geographic distribution and microhabitat. Seeds exposed to heat shocks above 80 °C lost viability, but smoke accelerated germination. We found a moderating effect of seed mass for responses to light and heat shocks, with larger, dormant seeds tolerating heat better but being less sensitive to light. Species from xeric habitats evolved phenological strategies to synchronize germination during periods of increased soil water availability.

Phylogenetic relatedness plays a major role in shaping the seed ecology of Brazilian rock outcrop vegetation. Nevertheless, seed traits and germination responses varied significantly between growth forms, species geographic distribution and microhabitats, providing support to the regeneration niche hypothesis and the role of functional traits in shaping germination in these ecosystems.